Although black Americans are particularly susceptible to develop essential hypertension, the causes of these high morbidity rates are unclear. Research has documented the potential importance of beta-adrenergic cardiovascular and neuroendocrine hyperresponsivity to stress in hypertension development, particularly among those with a parental history of hypertension. This beta-adrenergic response pattern is characterized in part by increases in heart rate, blood pressure, and muscle vasodilatation ("defense pattern"). Yet, data from a variety of sources suggests that blacks at risk for hypertension may evidence reduced rather than augmented beta-adrenergic tone compared to whites. At the same time, however, blacks may be more sensitive to stressors which produce alpha-mediated cardiovascular responsivity and muscle vasoconstriction. Three proposed studies are designed to determine whether blacks at risk for hypertension, compared to whites, exhibit different levels of cardiovascular reactivity to a stressor known to produce the defense reaction with muscle vasodilatation (mental arithmetic) vs. one which produces muscle vasoconstriction (ice applied to the forehead). In the first study, young black and young white males (aged 18-24) will be studied. Half of the subjects in each group will have a documented parental history of hypertension. Studies two and three will use as subjects young black females and middle-age black males (35-45), respectively. The methodology for each study will be identical. Measurements of heart rate, blood pressure, and forearm blood flow will be obtained during mental arithmetic, and during the application of an ice pack to the forehead. It is expected that during mental arithmetic, black subjects with a parental history of hypertension will exhibit a smaller defense pattern than their white counterparts. During the cold stress however, black subjects with a parental history of hypertension should exhibit larger muscle vasoconstriction and blood pressure responses compared to their white counterparts. If it can be demonstrated that blacks at risk for hypertension exhibit diminished vasodilatation and enhanced vasoconstriction to stress, then this would suggest the presence of important racial differences in hemodynamic mechanisms which may contribute to the pathogenicity of essential hypertension.